One problem particularly involved in paystation telephone operation has been that of acoustic isolation between the transmitter and receiver, this being necessary for the prevention of the receiver being used as a transmitter during periods when the transmitter is disabled for control purposes. One method of dealing with this problem has been the inclusion of an isolation amplifier separating the two, this amplifier being connected between the transmission network receiver output and the handset receiver.
A further problem has been that of preventing a user from recording tones generated in response to the insertion of discrete denominations of coins with respect to which the recording might later be used to make calls without payment.
Another problem has been that of reducing, to below annoying levels, the level in the receiver of dialing tones used in many telephone systems.
Still another problem has been that of conveniently and effectively providing appropriate communication or voice sound levels for paystation users having hearing defects. Presently, and in recognition of this problem, some paystation phones have been equipped with induction coils for direct coupling to hearing aids. However, not all hard of hearing customers have hearing aids. To meet this problem, some paystations have been equipped with separate dedicated amplifiers to provide a boost of acoustic output.
In recognition of the foregoing, it is the object of this invention to provide an improved level control which deals with all of the level requirements present in a single signal level control system.